Reverberation Mapping of the Intermediate Mass Nuclear Black Hole in SDSS J114008.71+030711.4

TL;DR

This study uses reverberation mapping to estimate the size and mass of an intermediate-mass black hole in an active galaxy, finding a smaller-than-expected BLR size and a low black hole mass estimate, suggesting super-Eddington accretion.

Contribution

First reverberation mapping measurement of an intermediate-mass black hole in SDSS J114008.71+030711.4, providing new constraints on BLR size and black hole mass in such objects.

Findings

Measured reverberation lag of 2 days, upper limit 6 days.

Estimated black hole mass less than 5.8 x 10^5 solar masses.

Observed BLR size smaller than predictions from standard R-L relation.

Abstract

We present the results of a reverberation mapping (RM) campaign on the black hole (BH) associated with the active galactic nucleus (AGN) in SDSS J114008.71+030711.4 (hereafter GH08). This object is selected from a sample of 19 candidate intermediate mass BHs (M_{BH} < 10^{6} Msun) found by Greene & Ho 2004 in the Sloan Digital Sky Survey (SDSS). We used the Hobby-Eberly Telescope to obtain 30 spectra over a period of 178 days in an attempt to resolve the reverberation time lag (tau) between the continuum source and the broad line region (BLR) in order to determine the radius of the BLR (R_{BLR}) in GH08. We measure tau to be 2 days with an upper limit of 6 days. We estimate the AGN luminosity at 5100 Angstroms to be approximately 1.1 x 10^{43} erg s^{-1} after deconvolution from the host galaxy. The most well calibrated R_{BLR}-L relation predicts a time lag which is 4 times larger than what we measure. Using the measured H\beta\ full-width-at-half-maximum of 703 (+/-) 110 km s^{-1} and an upper limit for R_{BLR} = 6 light days, we find M_{BH} < 5.8 x 10^{5} Msun as an upper limit to the BH virial mass in GH08, which implies super-Eddington accretion. Based on our measured M_{BH} we propose that GH08 may be another candidate to add to the very short list of AGNs with M_{BH} < 10^{6} Msun determined using RM.